Introduction to Drilling and Openhole Logging

October 2011

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DRILLING OPERATION

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Depth of Water Dictates Offshore Rig Type

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Electronics inside an LWD Tool

LWD refers to Logging While Drilling

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Drilling bits

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Role of Drilling In Field Development

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Personnel Involved In Drilling A Well

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Proposal For Drilling

• Proposal for drilling – prepared by the geologist and reservoir engineers

• Provides information upon which well will be designed and the drilling program.

• Contain:

– Objective of the Well

– Depth and location of target

– Geological cross section

– Pore pressure profile prediction

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Drilling Program

• Drilling program is prepared by the Drilling Engineer

• Containing: – Drilling rigs to be used for the well

– Proposed location for the drilling rig

– Hole sizes and depths

– Casing sizes and depths

– Drilling fluids specifications

– Directional drilling information

– Well control equipment and procedures

– Bits and hydraulic program

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• Rotary drilling is the technique whereby the rock cutting tool is suspended on the end of hollow pipe, so that fluid can be continuously circulated across the face of the drillbit cleaning the drilling material from the face of the bit and carrying it to surface.

• To be covered more in Drilling and Production Technology

Drilling Rig

Drilling Rig

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Drilling Fluid

Whilst drilling the a hole, drilling fluid (mud) is circulated down the drillpipe, across the face of the drillbit, and up the annulus between the drillpipe and the borehole, carrying the drilled cuttings from the face of the bit to surface. At surface the cuttings are removed from the mud before it is circulated back down the drillpipe, to collect more cuttings.

Mud

• Used as a carrying agent

• Balance the formation pressure

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Conductor

Surface casing

Intermediate casing

Production casing

Production liner

Introduction to Drilling

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Typical Sequence of Operations :

• Rig up

Sea level

Cellar deck

Main deck

Conductor depth reference

Depth reference below derrick floor - bdf roller kelly bushing - rkb

Drilling Process

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Typical Sequence of Operations :

• Rig up • Pile Conductor Casing

Sea level

Cellar deck

Main deck

Conductor

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole • Run and set production casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole • Run and set production casing • Cement casing

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole • Run and set production casing • Cement casing • Drill production hole

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole • Run and set production casing • Cement casing • Drill production hole • Run and set liner

Drilling Process

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Typical Sequence of Operations :

• Rig up • Drill surface hole • Run and set surface casing • Cement casing • Drill intermediate hole • Run and set intermediate casing • Cement casing • Drill production hole • Run and set production casing • Cement casing • Drill production hole • Run and set liner • Cement liner

Drilling Process

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Typical Hole and Casing Size

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Drilling Rigs

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Drilling Fluids

• Types

– Water-based mud (WBM)

– Oil-based mud (OBM)

• Functions:

– Remove cuttings from the wellbore

– Prevent formation fluids flowing into the wellbore

– Maintain wellbore stability

– Cool and lubricate the bit

– Transmit hydraulic horsepower to bit

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• Drill mud should be able to:

– Carry cuttings to the surface while circulating

– Suspend the cuttings while not circulating

– Drop cuttings out of suspension at surface

• Selection considerations

– Environmental impact of the fluids

– Costs

– Impact of the fluids on production from the payzone

Drilling Fluids

Well Control

• The purpose of well control is to ensure that fluid (oil, gas and water) does not flow in an uncontrollable way from the formations being drilled, into the borehole and eventually to surface.

• This flow will occur if the pressure in the pore space of the formation being drilled (the formation pressure) is higher than the hydrostatic pressure exerted by the column of mud in the wellbore

• It is essential that the borehole pressure exceeds the formation pressure but below __________ pressure at all times during drilling.

• If formation pressure is greater than the borehole pressure an influx of fluid into the borehole will occur. Well taken a _________ .

• If no action is taken to stop the influx of fluid once it begins, then drilling mud will be pushed out of the borehole and the formation will be flowing in an uncontrolled manner at surface known as __________.

Definition

• Kick

– An unwanted influx of formation fluids into the wellbore

• Blowout

– An uncontrolled flow of wellbore fluids

Well Control Principle

• Primary Control – Pressure exerted by column of mud in the

borehole is greater than the pressure in the formations being drilled

• Secondary Control – Primary control fail

– The aim of secondary control is to stop the flow of fluids into well bore and eventually allow the influx to be circulated to surface and safely discharge, while preventing further influx down hole

Primary Control – Pressure due to mud Colum exceed pore pressure -

Secondary Control – Influx

controlled by closing BOP’s

Well Control Principle

The bore hole pressure becomes less than the formation pressure in two ways : 1. The formation pressure in a zone which penetrated is

higher than that predicted by reservoir engineer and geologist.

2. The pressure due to the colum of mud decreases for some reason and bottom hole pressure drops below the formation pressure.

p = 0.052 x mw density x height of mud colum

Equivalent Circulating Density (ECD)

• The pressure provided by the rig pump is the sum of all of the individual pressure in the circulating system

• Overcoming friction losses between mud and whatever it is in contact with results is; – Pressure loss in surface line – Pressure loss in drill string – Pressure loss across bit nozzle – Pressure loss in annulus

• Pressure losses in the annulus acts as a backpressure to the formation, consequently the total pressure at the bottom hole is higher with the pump is on than with the pump off.

• ECD = Static bottom hole pressure + annulus pressure losses

CASING SETTING DEPTHS

• Main factors that govern the setting depths are:

– Formation pressures (normally, abnormally)

– Fracture Pressures

– Government Legislation or Company Policy

• Casing setting depths are selected for the deepest string to be run and then successively from the base of the well to surface

• The first selection criteria for selecting deeper setting depths is to permit the mud weight to control formation pressures without fracturing any overlying formations

• Plot pressure (pore, fracture and mud weight) against depth profile

CASING SETTING DEPTHS (cont’d)

CASING SETTING DEPTHS (cont’d)

Required mud density to drill to “a”

Prodn casing is set here

Intermediate casing is set here to prevent fracturing

Required mud density to drill to “c”

Surface casing is set here to prevent fracturing

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Directional Drilling

• Reasons for Drilling a non-vertical (deviated well)

– Multi-well platform drilling

– Fault Drilling

– Inaccessible locations

– Sidetracking and straightening

– Salt dome drilling

– Relief wells

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Directional Drilling

• Multi-well platform drilling

– Feasible in drilling a large number of wells from one locations (platform)

– Deviated well are designed to intercept a reservoir over a wide aerial extend.

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• Fault drilling

– To avoid damage by fault slippage

– Can be minimize by drilling parallel to a fault and then changing the direction of the well across the target

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• Inaccessible locations

– To avoid obstacle at surface (eg. River, mountain range, city)

– A well directionally drilled into the target from distance away form the point vertically above the required point of entry into the reservoir

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• Sidetracking and straightening

– To correct the course of the well

– In the event of drillpipe stuck in the hole, alternative course required.

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• Salt dome drilling

– To recover the accumulated hydrocarbon beneath the flank of the salt dome

– To avoid potential problems (eg. Severe washout, moving salt, high pressure of dolomites)

– Well is drilled alongside the salt dome to reach the reservoir

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• Relief wells

– In the event of blow-out, the rigs is damaged.

– To kill the ‘wild’ well, another directionally drilled well is required.

– ‘Wild’ well can be killed by circulating high density fluid down the relief well, into and up the wild well.

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Well Logging Operation

• Openhole wireline well logs are recorded when the drilling tools are no longer in the hole.

• They are recorded immediately after drilling and before the casing setting.

• MWD (measurement while drilling) or LWD (logging while drilling) logs, by contrast, are made as a formation is drilled.

• The first logging toll is attached to the logging cable and lowered into the hole to its maximum drilled depth.

Cost Versus Information Collected

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Drilling (10%)

Logging (90%)

Geological Information Cost (%)

(Source: Serra, 2003)

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• Onshore, Wireline electrical logging is done from a logging truck sometimes referred to as a mobile laboratory

• Offshore, the same equipment is installed in a small cabin left permanently on the rig.

• Both truck and cabin use a variety of interchangeable logging tools, which are lowered into the well on the logging cable.

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• Most logs are run while pulling the tool up from the bottom of the hole.

• The cable attached to the tool acts both as

support for the tool and as a canal for data transmission.

• The outside consists of galvanized steel, while the electrical conductors are insulated in the interior.

• The cable is wound around a motorized drum on to which it is guided manually during logging.

• The drum will pull the cable. As the cable is pulled in, so the depth of the working tool is checked.

• Logging cables have magnetic markers set at regular intervals along their length and depths are checked mechanically, but apparent depths must be corrected for cable tension and elasticity

Logging operation

• Logging units, drill floor, catwalk

• 3 types of logging:

– Mudlogging – more in the next class

– M/LWD – what, how, why

– Wireline logging – what, how, why

MUD LOGGING

MWD or LWD

• MWD

– Survey + GR? + Resisitivity?

• LWD

– Survey + GR + Res + Density + Neutron…

Wireline logging

Wireline logs – ie..

• GR • Resistivity • Sonic • Density • Neutron • Imaging • Sidewall core • Formation pressure & fluid sampling • Vertical seismic • …

Logging operation..

• Tool calibration

• Rig up, RIH, log, POOH, download data

• Rathole

• Log up, logging speed

• Repeat section

• Depth reference – SS, RT, DFE

• MD vs TVD

• Resolution vs depth of investigation

Depth in logs

• Ft/m

• MD/TVD

• Usually in log correlation.. mSS

– TVD-DFE

– Reference to MSL, not ML

TOOL COMBINATIONS

DEPTH OF INVESTIGATION & RESOLUTION

THE LOG

CORING

CORE ANALYSIS

conventional coring

Sidewall coring

Drilling to PNA

• Drill

• Case

• Cement

• LOT, drill ahead, repeat

• Log

• Case

• Cement

• Test?

• PNA

Well plan and drilling activities

Group exercise

• 6 groups – each group must have

– Girls, boys, >1 nationalities, >5 states

• Write name & details behind question paper (14-15 pax/group)

• 20-30 mins prepare

• Selected presenter

Q1

• Which is the correct well profile? Why? Explain briefly how a well is drilled..

Q2

• Draw, label the main components of a drilling rig

• Discuss the use/relevance to drilling & logging operation

Q3

• Define & differentiate LWD and Wireline logging

• Discuss their pros & cons

• Which is better?

Q4

• You are logging a deviated well on an offshore jack-up rig with the following details:

• Sketch your depth references and label the followings: – MSL 150m

– DFE 50m

– TD at 1500 mMD, 1200mTVD

• What is the TD of your log in mSS?

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• Explain why do we sometimes combine logging tools for the same run.

• Would you combine sampling tool & sonic tool? Discuss.

• Sketch a logging tool with following combination- ie. – Tool zero – Resistivity (15m) –

Density (20m) – Neutron (25m) – GR (27m) - tool head (30m)

– How much of a rathole would you need?

Q6

• What is the most common use of log data by a geologist?

• What is the most common use of log data by a reservoir engineer?

• Hypothetically, consider why a 6-ft thick oil sand in a well at 10000-ft depth would be considered noncommercial, but a 6-ft oil sand in a well at 1000-ft depth would be considered commercial?

• As a log user, why is it important that you know and understand the drilling & logging operation?

For geologists:

• formation tops/depth,

• thickness,

• for correlations, cross sections, structural and isopach maps, depositional model

For reservoir engineers:

• besides geological model

• petrophysical parameters =

– porosity,

– permeability,

– Shc,

– HC type,

– viscosity..

• For volumetrics & producibility